Ajax ModelpopupExtender Cant work - asp.net

Question

I am using modelpopupextender in asp.net and this code is working window is popup sucessfuly but cancel button can't work; can anybody tell me why?
<%# Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp"
%>
<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</asp:ToolkitScriptManager>
<asp:Button ID="buttonOpen" runat="server" style="display:none" ></asp:Button>
<asp:Panel ID="Panel3" runat="server" BackColor="#99CCFF" Height="269px" Width="350px"
style="display:none">
<table width="100%" style="border:Solid 3px #D55500; width:100%; height:100%"
cellpadding="0" cellspacing="0">
<tr style="background-color:#333399">
<td colspan="2" style=" height:10%; color:White; font-weight:bold; font-size:larger"
align="center">Time Details</td>
</tr>
<tr>
<td>
<asp:Label ID="Label19" runat="server" Text="Time From"></asp:Label>
</td>
<td>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<asp:Label ID="Label20" runat="server" Text="Time To"></asp:Label>
</td>
<td>
<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<asp:Label ID="Label21" runat="server" Text="Number of Slots"></asp:Label>
</td>
<td>
<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<asp:Button ID="Button1" runat="server" Text="Add" />
</td>
<td>
<asp:Button ID="btnCancel" runat="server" Text="Cancel" />
</td>
</tr>
</table>
</asp:Panel>
<asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server" OnCancelScript="btnCancel" PopupControlID="panel3" TargetControlID="buttonOpen" BackgroundCssClass="modalBackground">
</asp:ModalPopupExtender>

Answer 1

You need to set the CancelControlID property, not the OnCancelScript property (unless you want to execute a script after the cancel button is clicked). So for your scenario, do this:
<asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server" CancelControlID="btnCancel" PopupControlID="panel3" TargetControlID="buttonOpen" BackgroundCssClass="modalBackground">
</asp:ModalPopupExtender>